Structure and Function of Structure and Function of Forest TreesForest Trees

Kenneth WilliamsFisheries Extension Specialist Langston University Aquaculture Extension Program

Elements of Forestry

TreesTreesLongest lived organisms on earth.Heights of 100 meters diameters of 10

meters.Due to longevity, trees must withstand

extremes of climate.Trees allocate much of their energy to

diameter growth. Not so in other plants.Physiology of trees a young science.

3 TISSUE SYSTEMS OCCUR IN 3 TISSUE SYSTEMS OCCUR IN PLANTSPLANTS

Dermal Tissue System– Function: Protection from the environment and

water loss.  

Vascular Tissue System– Function: Conduction of water, nutrients, sugars

and hormones throughout the plant. 

Ground or Fundamental Tissue System– Function: Storage, support, filler tissue and site of

photosynthesis. 

Dermal Tissue SystemDermal Tissue System

Function: Protection from the environment and water loss.  

Tissues:   a) epidermis - single layer of cells on

primary (herbaceous ) plant parts.   b) periderm or bark - a corky tissue that

replaces epidermis on secondary (woody) plant parts. 

Vascular Tissue SystemVascular Tissue System    

Function: Conduction of water, nutrients, sugars and hormones throughout the plant.  

Tissues:   a) xylem - conducts water and nutrients up

roots, stems and leaves.   b) phloem - conducts water, sugar, hormones,

etc. primarily down roots, stems and leaves,  but also can move up at times. 

Ground or Fundamental Tissue Ground or Fundamental Tissue SystemSystem

Function: Storage, support, filler tissue and site of photosynthesis.  

Tissues:    a) cortex - outer region of stems and

roots.   b) pith - center of stems. c) mesophyll - middle of leaves and

flower petals

PLANT ORGANS, TISSUE SYSTEMS, TISSUES AND CELL TYPES   3 TISSUE SYSTEMS OCCUR IN PLANTS  Dermal Tissue System   Function: Protection from the environment and water loss.   Tissues:   a) epidermis - single layer of cells on primary (herbaceous ) plant parts.   b) periderm or bark - a corky tissue that replaces epidermis on secondary

(woody) plant parts.  2) Vascular Tissue System   Function: Conduction of water, nutrients, sugars and hormones throughout the

plant.   Tissues:   a) xylem - conducts water and nutrients up roots, stems and leaves.   b) phloem - conducts water, sugar, hormones, etc. primarily down roots, stems

and leaves,  but also can move up at times.  3) Ground or Fundamental Tissue System   Function: Storage, support, filler tissue and site of photosynthesis.   Tissues:    a) cortex - outer region of stems and roots.   b) pith - center of stems.  c) mesophyll - middle of leaves and flower petals

MERISTEMS AND GROWTH   Primary Growth - growth in length that gives rise

to primary (herbaceous) tissues called the primary plant body.

Apical meristem or apex - the growing points located at the tips of stems and roots

        Secondary Growth - growth in width or diameter

that gives rise to secondary (woody or corky) tissues called the secondary plant body.

Apical meristemApical meristem

Shoot diagramShoot diagram

Shoot growthShoot growth

Fixed shoot growth – 1 period of spring growth, often over quickly. Ex. Dogwood.

Free shoot growth – continual growth throughout season (most in spring) ex. Cottonwood

Recurrent flushing – several periods of growth throughout season. Ex. White oak

Shoot growthShoot growthFree growth – fast growing hardwoods –

poplar, willow, cottonwood and sweetgum.Fixed growth – slower growing hardwoods

and conifers – northern oak, sugar maple, white pine.

Free growthEx. willow

Fixed growth Ex. Red oak

Recurrent flushing – several periods of growth throughout season. Ex. White oak and fast growing conifers ex. Red pine.

Each growth spurt ends in new bud formation. Then the new buds grow in the next cycle 3-7

times per year.

Root growthRoot growth

Similar to shootsTaproot is the 1st root to grow. Branch roots

form off of it. Taproot may not persist.Root growth depends on soil and moisture

conditions/ Ex. Red maples on upland sites have large taproots but have a shallow rot system in poorly drained soils.

Root growthRoot growth

Most growth in length occurs in the long roots.

Most surface area is in the short of fine roots. The fine roots are also called feeder roots. They take up nearly all the water and nutrients.

Larger roots provide a conduction path and mechanical support.

Fine roots, the mycorhizaeFine roots, the mycorhizae

Most of the fine roots are actually a fungus called mycorhizae plus tissues from the tree root.

Mycorhizae increase root surface area, increase water and nutrient uptake and increase resistance to pathogens and nematodes.

Fine roots, the mycorhizaeFine roots, the mycorhizae

The mycorhizae receive most of its food from the host tee.

This is a very important fungal/tree partnership and crucial to tree survival.

All trees are mycorhizalWithout this fungus trees will stunt and may

die.

Root growthRoot growthMychorrizal

fungi

Flowering and reproductionFlowering and reproduction

Flowers develop as vegetative shoot apical meristem transforms into a reproductive meristem.

Flower shoots have a determinate growth pattern, they grow, flower and meristem disappears.

Conifer reproductionConifer reproduction Male and female cones are borne

separately on the same tree. Male cones are usually lower than

female cones to reduce self pollination.

Male cones are small (1-2 cm) release pollen in spring 1 year after forming.

Female cones large, seeds released 2 years after pollination.

Conifers are wind pollinated

Angiosperm reproductionAngiosperm reproduction

Pollination may be by wind, insects, birds or bats.

Flower and seed development may be in a few weeks ex. Poplars or several years, ex. Some oaks.

Male and female reproductive parts may be in the same flower or male and female flowers on separate trees.

Angiosperm reproductionAngiosperm reproduction

Seeds dispersed in spring can usually germinate immediately. Ex .silver maple

Many trees disperse seeds in fall and winter. These seeds remain dormant until spring. Ex. Some oaks

Some seeds can remain in the soil for years until conditions are right for germination.

Secondary growthSecondary growth

Diameter growth occurs In the vascular cambium, the large sheet of cells below the bark.

It ensheaths the entire plant body in a single layer of cells..

During growth cambium divides to produce xylem to the inside and phloem to the outside of this tissue.

Secondary growthSecondary growth

Cambium activity is greater in spring than summer making the cells at this time larger.

This results in annual rings. Usually 1 ring per year.

Rings may be missing or incomplete or sometimes more than 1 per year.

Cross sectionCross section

Cross sectionCross section

Cross sectionCross section

XylemXylem3 functions: Conduction of water by cells called

vessels. These cells are dead.Support by thick walled vessel cells.Storage – parenchyma cells transport and

store starches. These cells may be in rays.Hardwoods more efficient than conifers in

moving water due to structural differences.

HeartwoodHeartwood

Healthy heartwood (dead parenchyma cells)

Fungus rotted heartwood

Sapwood (living parenchyma cells) can be 300 yr. old

PhloemPhloem

Cells form sieve tubes – vertically arranged files of living cells with end walls that are porous.

Phloem transports sugars and organic substances formed in leaves to other parts of the tree and roots.

Phloem is only functional a few years before the cells are crushed in tree growth

Xylem and Xylem and phloemphloem

TracheidsTracheidsSimilar function as xylem in hardwoods, support and conduction

Cork cambium and barkCork cambium and bark

Periderm or outer bark formed from the cork cambium which originates in the epidermis.

Cells to the outside of the cork cambium have a thick layer of a waxy substance called suberin.

Suberin is water repellant and resistant to bacteria and fungus.

New periderms are continuously formed. Cork cells are dead at maturity.

CambiumCambium

Cork Cork cambium cambium of cork of cork

oakoak

Leaf structureLeaf structure

Gas movement through leavesGas movement through leaves

RespirationRespiration

Respiration provides energy for growth, maintenance and the construction of new cells.

Respiration is the opposite of photosynthesis. The oxidation of sugars o carbon dioxide and water, releasing usable chemical energy.

RespirationRespirationThe chemical equation for respiration is:(CH2O)6 + 6 O2 6 CO2 + 6 H2OPhotosynthesis occurs mostly in leaves.Respiration occurs in all living cells.Carbohydrates not used in respiration are

stored as starches. An important tree reserve.

Many trees have enough stored starch to re-foliate the tree 3 times. This allows the tree to recover from insect, weather and disease damage.

Growth Growth substances or substances or plant plant hormoneshormones

Effects very Effects very complex and complex and not always not always understood.understood.

Secondary compoundsSecondary compounds

1000’s of chemicals produced by trees, many with no known function.

Some may be defensive.Many have commercial value, ex. The

terpenoids.

WaterWater

Single most important factor in tree growth and survival.

Water makes up 80% of living cells.Most water in trees lost through

transpiration.There is a continuous column of water from

soil to roots to leaves in trees. This is called the soil-plant-atmosphere continuum.

TranspirationTranspiration

MacronutrientsMacronutrients

MicronutrientsMicronutrients

LightLight

Shade tolerance – ability of a tree to grow in the shade of other trees.

Photoperiod – duration of daylight. Provides signals for bud set and leaf fall and other physiological functions.

TemperatureTemperature

Trees grow between 0C – 40CThey become dormant when temperatures

begin to drop.

Tree formsTree forms

Excurrent growth form – single main stem ex. Pine tree.

Decurrent growth form – multiply stems, ex. Elm tree.

Tree formsTree forms

Decurrent growthExcurrent growth

Tree longevityTree longevity

Oldest bristlecone pine – 4844 years oldFound in Nevada 1965.

Tree longevityTree longevity

Growth rate slows as trees age.They become less resistant to pests and

disease.May be killed from storms , fungal rot etc.Physiology of tree longevity poorly

understood.

Giant sequoia over 300 ft. high

Largest treesLargest trees

THE ENDTHE END